Iron powder composition

ABSTRACT

A powder composition for warm compaction comprising an iron-based powder and a lubricant powder consisting essentially of an amide described by the following formula D—C m —B—A—B—C m —D wherein D is —H, COR, CNHR, wherein R is a straight or branched aliphatic or aromatic group including 2-21 C atoms; C is the group —NH(CH) n CO—; B is amino or carbonyl; A is alkylene having 4-16 C atoms optionally including up to 4 O atoms m is an integer 1-10 and n is an integer 5-11.

FIELD OF THE INVENTION

[0001] The present invention relates to metal powder compositions. Particularly the invention relates to iron-based compositions suitable for compaction at elevated temperatures.

BACKGROUND OF THE INVENTION

[0002] The powder metallurgy art generally uses different standard temperature regimes for the compaction of a metal powder to form a metal component. These include chill-pressing (pressing below ambient temperatures), cold-pressing (pressing at ambient temperatures), hot-pressing (pressing at temperatures above those at which the metal powder is capable of retaining work-hardening), and warm-pressing (pressing at temperatures between cold-pressing and hot-pressing).

[0003] Distinct advantages arise by pressing at temperatures above ambient temperature. The tensile strength and work hardening rate of most metals is reduced with increasing temperatures, and improved density and strength can be attained at lower compaction pressures. The extremely elevated temperatures of hot-pressing, however, introduce processing problems and accelerate wear of the dies. Therefore, current efforts are being directed towards the development of metal compositions suitable for warm-pressing processes.

[0004] The U.S. Pat. No. 4,955,789 (Musella) describes warm compaction in general. According to this patent, lubricants generally used for cold compaction, e.g. zinc stearate, can be used for warm compaction as well. In practice, however, it has proved impossible to use zinc stearate or ethylene bisstearamide (commercially available as ACRAWAX®.), which at present are the lubricants most frequently used for cold compaction, for warm compaction. The problems, which arise, are due to difficulties in filling the die in a satisfactory manner.

[0005] The U.S. Pat. No. 5,744,433 (Storstrom et al) and U.S. Pat. No. 5,154,881 (Rutz) disclose metal powder compositions including amide lubricants which are especially developed for warm compaction.

[0006] The lubricant according to the U.S. Pat. No. 5,744,433 contains an oligomer of amide type, which has a weight-average molecular weight Mw of 30,000 at the most. Very high densities and green strengths may be obtained by warm compacting powder compositions when the lubricant has a molecular weight above 4000, the preferred lubricant molecule having a molecular weight of about 6500. It has however been found that this lubricant has a tendency of sticking to the die wall, which requires frequent cleaning of the die. Another disadvantage is that the obtained green bodies are stained.

[0007] In the U.S. Pat. No. 5,154,881 the amide lubricant consists of the reaction product of a monocarboxylic acid, a dicarboxylic acid and a diamine. The only lubricant tested according to this patent is ADVAWAX® 450, the composition of which is not described in detail but the reaction product obtained includes i.a. ethylene bisstearamide according to Chemis-CIVS. Our experience of this product is that it is difficult to obtain a constant composition and quality, which in turn may result in components of varying quality. This is may cause problems when the lubricant is used in large scale industrial production.

OBJECTS OF THE INVENTION

[0008] An object of the present invention is to reduce or eliminate current problems associated with large scale production.

[0009] A second object is to provide a new type of lubricant useful in metal compositions intended for compaction at elevated temperatures.

[0010] A third object is to provide a metal powder for producing components without stains.

[0011] A fourth object is to provide a metal composition including lubricant, which during the compaction of the metal powder does not deposit on the die wall.

SUMMARY OF THE INVENTION

[0012] These objects are achieved by using a powder composition comprising an iron-based powder and new oligomer amide type lubricant. The composition may also include one or more additives, such as binders, flow agents, processing aids and hard phases.

[0013] The warm compaction may be performed by mixing an iron-based powder with the oligomer amide type lubricant and optionally a binder, preheating the powder composition and compacting the metal-powder composition in a pre-heated tool.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The new amide type lubricant used according to the present invention may be represented by the following formula

D—C_(m)—B—A—B—C_(m)—D

[0015] wherein

[0016] D is —H, COR, CNHR, wherein R is a straight or branched aliphatic or aromatic group including 2-21 C atoms

[0017] C is the group —NH(CH)_(n)CO—

[0018] B is amino or carbonyl

[0019] A is alkylen having 4-16 C atoms optionally including up to 4 O atoms

[0020] m is an integer 1-10

[0021] n is an integer 5-11.

[0022] It is preferred that D is COR, wherein R is an aliphatic group 16-20 C atoms, C is —NH(CH)_(n)CO— wherein n is 5 or 11; B is amino; A is alkylene having 6-14 C atoms optionally including up to 3 O atoms, and m is an integer 2-5.

[0023] Examples of preferred lubricants to be used in the iron based compositions according to the present invention are:

[0024] CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₂—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₂—OC(CH₂)₁₆CH₃

[0025] CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₂—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₃—OC(CH₂)₁₆CH₃

[0026] CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₃—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₃—OC(CH₂)₁₆CH₃

[0027] CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₃—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₄—OC(CH₂)₁₆CH₃

[0028] CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₄—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₄—OC(CH₂)₁₆CH₃

[0029] CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₄—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₅—OC(CH₂)₁₆CH₃

[0030] CH₃(CH₂)₆CO—[HN(CH₂)₁₁CO]₅—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₅—OC(CH₂)₁₆CH₃

[0031] The chemical differences between the new lubricant and the lubricant described in the U.S. Pat. No. 5,744,433 are that the new molecule has a central diamine or diacid moiety and identical terminal groups on both ends. The difference between the new lubricant and the lubricant described in the U.S. Pat. No. 5,154,881 is that the new lubricant molecule includes the unit —NH(CH)_(n)CO—.

[0032] As regards the molecular weight of the new lubricant molecule it has been found that the preferred lubricants have a molecular weight between 1000 and 5000, most preferably between 1500 and 3000.

[0033] The lubricant molecule may be prepared according standard procedures for amide oligomer as described in e.g. “Principles of Polymerization” third edition by George Odian (John Wiley & Sons, Inc.).

[0034] As used in the description and the appended claims, the expression “iron-based powder” encompasses powder essentially made up of pure iron; iron powder that has been prealloyed with other substances improving the strength, the hardening properties, the electromagnetic properties or other desirable properties of the end products; and particles of iron mixed with particles of such alloying elements (diffusion annealed mixture or purely mechanical mixture). Examples of alloying elements are copper, molybdenum, chromium, manganese, phosphorus, carbon in the form of graphite, and tungsten, which are used either separately or in combination, e.g. in the form of compounds (Fe₃ P and FeMo). Unexpectedly good results are obtained when the lubricants according to the invention are used in combination with iron-based powders having high compressability. Generally, such powders have a low carbon content, preferably below 0.04% by weight. Such powders include e.g. Distaloy AE, Astaloy Mo and ASC 100.29, all of which are commercially available from Hoganas AB, Sweden.

[0035] This lubricant, which is added to the iron-based powder is preferably in the form of a solid powder, can make up 0.1-1% by weight of the metal-powder composition, preferably 0.2-0.8% by weight, based on the total amount of the metal-powder composition. The possibility of using the lubricant according to the present invention in low amounts is an especially advantageous feature of the invention, since it enables high densities to be achieved.

[0036] Apart from the iron-based powder and the lubricant, the new powder composition may contain one or more additives such as binders, flow agents, processing aids and hard phases.

[0037] The binder may be added to the powder composition in accordance with the method described in U.S. Pat. No. 5,368,630 (which is hereby incorporated by reference) and may be organic compounds such as cellulose ester resins, hydroxyalkyl cellulose resins having 1-4 carbon atoms in the alkyl group, or thermoplastic phenolic resins.

[0038] A type of flow agent, which can be used according to the present invention, is disclosed in the U.S. Pat. No. 5,782,954 (which is hereby incorporated by reference). The flow agent, which is preferably a silicon dioxide, is used in an amount from about 0.005 to about 2 percent by weight, preferably from about 0.01 to about 1 percent by weight, and more preferably from about 0.025 to about 0.5 percent by weight, based on the total weight of the metallurgical composition. Furthermore, the flow agent should have an average particle size below about 40 nanometers. Preferred silicon oxides are the silicon dioxide materials, both hydrophilic and hydrophobic forms, commercially available as the Aerosil line of silicon dioxides, such as the Aerosil 200 and R812 products, from Degussa Corporation.

[0039] The processing aids used in the metal-powder composition may consist of talc, forsterite, manganese sulphide, sulphur, molybdenum disulphide, boron nitride, tellurium, selenium, barium difluoride and calcium difluoride, which are used either separately or in combination.

[0040] The hard phases used in the metal-powder composition may consist of carbides of tungsten, vanadium, titanium, niobium, chromium, molybdenum, tantalum and zirconium, nitrides of aluminium, titanium, vanadium, molybdenum and chromium, Al₂ O₃, and various ceramic materials.

[0041] The invention is further illustrated by the following examples which are to be interpreted only as examples but should not limit the scope of protection.

EXAMPLE 1

[0042] The following tables disclose a comparison of properties between components prepared from powder mixtures including the lubricant according to the present invention and the amide type lubricant disclosed in the U.S. Pat. No. 5,744,433. TABLE 1 Compaction Ejection Ejection Spring- Pressure GD Force Energy back Lubricant (MPa) (g/cm³) (N/mm²) (J/cm²) (%) Invention 500 7.14 11.5 19.3 0.147 ″ 600 7.29 11.4 23.3 0.162 ″ 700 7.38 11.8 24.6 0.192 Orgasol 500 7.09 11.9 29.9 0.191 3501* 600 7.22 13.8 40.0 0.187 700 7.30 16.0 48.5 0.229

[0043] TABLE 2 Compaction Pressure Appearance Lubricant (MPa) Green compact Die Wall Invention 500 No stains No deposit ″ 600 Few stains No deposit ″ 700 Few stains No deposit Orgasol 500 Many stains Some deposit 3501* 600 Many stains More deposit 700 Many stains More deposit

[0044] The iron-based powder was Distaloy AE available from Höganäs AB, Sweden. This powder was mixed with 0.3% by weight of ultrafine graphite and 0.6% by weight of a lubricant according to the present invention. A flow enhancing agent Aerosil® 200 was added in an amount of 0.06% by weight.

[0045] As can be seen the new oligomer amide type lubricant according to the present invention is superior not only as regards the ejection force, the ejection energy, the springback but also when it comes to the appearance of the compacted component. Additionally the lubricant does not deposit on the die wall.

EXAMPLE 2

[0046] The following table discloses a comparison of properties between components prepared from powder mixtures including the lubricant according to the present invention and the amide type lubricant disclosed in the U.S. Pat. No. 5,154,881.

[0047] As can be seen the lubricant according to the present invention is superior as regards the ejection force, the ejection energy and the springback. TABLE 3 Ejection Ejection Spring- GD Force Energy back (g/cm³) (N/mm²) (J/cm²) (%) Lubricant 7.46 9.7 20.9 0.121 according to the present invention Lubricant 7.40 15.4 21.9 0.201 according to U.S. Pat. No. 5 154 881

[0048] Compaction pressure 700 MPa

[0049] Temperature powder/Die 130° C./150° C.

[0050] The iron-based powder was Distaloy AE available from Höganäs AB, Sweden.

[0051] This powder was mixed with 0.3% by weight of ultrafine graphite and 0.6% by weight of a lubricant according to the present invention. A flow enhancing agent Aerosil was added in an amount of 0.06% by weight.

EXAMPLE 3

[0052] The following example discloses a comparison of densities of green bodies obtained with the oligomer amide lubricants which are used according to the present invention and which have different molecular weights.

[0053] The iron-based powder was Distaloy AE available from Höganäs AB, Sweden.

[0054] This powder was mixed with 0.3% by weight of ultrafine graphite and 0.6% by weight of a lubricant according to the present invention. A flow enhancing agent Aerosil was added in an amount of 0.06% by weight.

[0055] The powder was heated to a temperature of 130° C. and the temperature of die was 150° C. The compaction pressure was 700 MPa. Molecular Weight of Lubricant GD (g/cm³) 2000 7,44 3000 7,41 4000 7,31 

1. A powder composition for warm compaction comprising an iron-based powder and a lubricant powder, said lubricant consisting essentially of an amide represented by the following formula D—C_(m)—B—A—B—C_(m)—D wherein D is —H, COR, CNHR, wherein R is a straight or branched aliphatic or aromatic group including 2-21 C atoms C is the group —NH(CH)_(n)CO— B is amino or carbonyl A is alkylen having 4-16 C atoms optionally including up to 4 O atoms m is an integer 1-10 n is an integer 5-11.
 2. A powder composition according to claim 1 wherein D is COR, wherein R is an aliphatic group 16-20 C atoms, C is —NH(CH)_(n)CO— wherein n is 5 or 11; B is amino; A is alkylen having 6-14 C atoms optionally including up to 3 O atoms, and m is an integer 2-5.
 3. A powder composition according to any one of the claims 1-2 wherein wherein the lubricant consists of a compound selected from the group consisting of CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₂—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₂—OC(CH₂)₁₆CH₃ CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₂—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₃—OC(CH₂)₁₆CH₃ CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₃—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₃—OCCH₂)₁₆CH₃ CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₃—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₄—OC(CH₂)₁₆CH₃ CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₄—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₄—OC(CH₂)₁₆CH₃ CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₄—HN(CH₂)₁₂N—[OC(CH₂)₁₁NH]₅—OC(CH₂)₁₆CH₃ CH₃(CH₂)₁₆CO—[HN(CH₂)₁₁CO]₅—HN(CH₂)₁₂NH—[OC(CH₂)₁₁NH]₅—OC(CH₂)₁₆CH₃
 4. A powder composition according to any one of the claims 1-3, wherein said amide has a molecular weight of 1500 to 3000 and is present in said composition in an amount of less than 1% by weight.
 5. A powder composition according to any one of the claims 1-4, wherein the lubricant powder is provided in a concentration 0.2 to 0.8% by weight of the composition.
 6. A powder composition according to any one of the claims 1-5, which additionally contains one or more additives selected from the group consisting of binders, processing aids, and hard phases.
 7. A powder composition according to any one of the claims 1-6, wherein said iron-based powder is compressible, and at least 80% by weight of said lubricant powder is made up of said amide oligomer.
 8. A powder composition according to any one of the claims 1-6, wherein said composition is essentially free from ethylenebisstearamide.
 9. A powder composition according to any one of the claims 1-8, characterized in that said iron-based powder has a carbon content of at most 0.04% by weight.
 10. A method for producing sintered products comprising: (a) mixing an iron-based powder with a lubricant powder as defined in the previous claims; (b) preheating the metal-powder composition, (c) compacting the metal-powder composition in a preheated tool, and optionally (d) sintering the compacted metal-powder composition at a temperature above 1050° C. to form a sintered product. 